The goal of the sloan_start_end_vertices algorithm[1, 2] is to find good start-
and end-vertices for the profile and wavefront reduction algorithm sloan_ordering.
The algorithm is similar to pseudo_peripheral_pair and also based on breadth_first_search.
With this breadth_first_search function a so-called rooted level structure (RLS)
is formed, where the vertices with the same distance to the starting vertex
are grouped together. The maximum number of vertices in one group is called
the width of the RLS. Sloan_start_end_vertices tries to find a pseudoperipheral
pair with a minimum RLS-width.

Parameters

For version 1:

Graph& g (IN)
An undirected graph. The graph's type must be a model of IncidenceGraph.

vertex_descriptor s (IN)
The starting vertex.

ColorMap color_map (WORK)
Used internally to keep track of the progress of the algorithm (to avoid visiting
the same vertex twice).